1. Field of the Invention
The present invention relates to step motor drive control circuits, which are applicable to image scanners and the like.
2. Description of the Related Art
Hitherto, bipolar driving of a step motor has been performed by controlling a p-channel switching device and an n-channel switching device. Thus, there has been a slight difference between the current waveform by p-channel switching when supplying an electric current to a motor winding and the current waveform by n-channel switching when drawing the electric current from the motor winding.
As a result, for example, half-step drive of a five-phase step motor causes uneven rotation of the motor, which appears every one-quarter cycle of a motor drive frequency, due to the difference between switching characteristics of the p-channel and the n-channel.
Image scanners used in color copying machines or other suitable devices preferably employ step motors as the primary drive source due to the necessity for high accuracy positioning. However, when an image is scanned using a motor having an uneven rotation characteristic as described above, vibrations are generated in the mechanism and fine details in the image become jagged. As a result, the quality of the scanned image is degraded.